Fights occur when two Pinatas have a conflict, and can also happen if they just don`t like each other. There are many species which are natural rivals like the Barkbark and the Kittyfloss, and they will always have a conflict. If you want to stop a fight, you could try hitting the pinata with a shovel or watering them with the watering can, but this can lower their happiness, or you could try building a fence around their enclosures. If you have a Bonboon in your garden, they can help to stop fights (but not all of them).